Abstract

The novel phase Na3Al5O2(OH)2(AsO4)4 was prepared by hydrothermal synthesis at 873 K and 0.15 GPa. Its crystal structure was determined using single-crystal X-ray diffraction data and refined against F2 to R = 0.021. The compound crystallizes in the orthorhombic space group Ibam, with unit-cell parameters a = 7.4614(8), b = 17.468(3), c = 11.282(1) Å, V = 1470.5(3) Å3, and Z = 4. The structure is dominated by chains parallel to [001] and built of Al octahedra sharing edges and corners. The As1-centered tetrahedra strengthen these chains, while the As2O4 tetrahedra unite them in a three-dimensional framework with channels filled by Na. The hydroxyl group bridging two Al atoms plays the role of a donor providing hydrogen bonding to the oxygen atoms at the vertices of the As1O4 tetrahedra. The compound is a new structural variety in the palermoite and carminite–attakolite families of phosphate and arsenate minerals. Taking into account the close topology we suggest uniting these minerals in one group. The geochemically plausible composition of the synthesized phase and its structural similarity with discussed minerals let anticipate its discovery in nature as a new representative within this family of minerals.